The bitterness in citrus juices is derived from bitter components such as flavanoids, predominantly naringin, and/or limonoids and their precursors, predominantly limonin. The presence of bitterness is often accentuated by processing of the fruit to juice or juice concentrate. For example, limonin is formed from its non-bitter precursor limonoic .alpha.-ring lactone, which is initially present in the albedo of citrus fruits. The formation of limonin from its precursor takes place in the presence of an acidic environment or upon heating. Therefore, processes of juice extraction, heat pasteurization and concentration, and storage of juice or concentrate result in limonin induced bitterness, especially in early season orange, navel orange and lemon juices. Thus, it would be desirable to have a process for removing bitterness from juice. Limonin levels in excess of about 6 parts per million (ppm) are detectable as bitterness by most of the population, 20 percent of the population can detect levels down to 2 ppm.
U.S. Pat. No. 4,514,427 discloses debittering and reducing the acidity of grapefruit juice by contacting the grapefruit juice with a weak base anion exchange resin in the freebase form. When processing many juices such as orange juice using this process, the anion exchange resin in the freebase form adsorbs a large amount of the citric acid in the juice, which causes the pH of the juice to become basic. The increase in pH of the juice may cause the denaturing of the proteins present in the juice and result in an inferior quality juice. In addition, these denatured proteins can form small gellular masses which embed themselves in the resin. The result is excess pressure buildup within the resin vessel which leads to premature work stoppage. The denatured proteins are very difficult to remove from the resin, thereby resulting in excessive resin replacement costs. Another problem with the anion exchange resin used in the above-described process is that it does not have a large enough capacity to remove enough bitter components to get below the consumer threshold level of 6 ppm in a single passage. Furthermore, if the weak base resin is not used in its freebase form, the weak base resin's capacity for bitter components is unacceptably low.
U.S. Pat. No. 4,439,458 discloses debittering citrus fruit juice by contacting the clarified juice (i.e., juice with the pulp removed by passing the juice through a centrifuge) with a polystyrene adsorbent copolymer, crosslinked with divinylbenzene. After contact with the adsorbent, the clarified citrus juice is recombined with the pulp. The problem with the above-described process is that although some of the bitter taste is removed, the limonin precursor is still present in the untreated pulp. Thus, the juice still has somewhat of a bitter taste, especially after subsequent processing. Another problem with the process described above is that prior to contact with a juice the adsorbent copolymer must be pretreated with a water-soluble alcohol to extract any residual monomers such as, divinylbenzene for the copolymer. At the present time, the juice plants are not equipped to handle flammable liquids in their plants, and to install such equipment would probably be cost prohibitive.
It would be desirable to provide an efficient and commercially viable process for selectively removing bitter components such as, limonin or naringin or its precursors from citrus fruit juices. This would provide for more complete removal of bitterness from the juices.